Ordered entries
Duplicates elements not allowed

LinkedHashMap<Integer, String> lhm = new LinkedHashMap<>();

lhm.clear();
// lhm.put(null, "a"); // OK
// lhm.put(0, null); // OK
lhm.put(0, "a");
lhm.put(44444, "c");
lhm.put(555555, "b");
lhm.put(3333, "d");
lhm.put(11, "f");
lhm.put(222, "e");
lhm.put(6666666, "g");

for (Map.Entry<Integer, String> entry : lhm.entrySet()) {
    System.out.println(entry.getKey() + " = " + entry.getValue());
}

Output:

0 = a
44444 = c
555555 = b
3333 = d
11 = f
222 = e
6666666 = g